Cherry-pick: ICU-21875 improve C API coverage

Upstream commit: https://github.com/unicode-org/icu/commit/bfca3ccaac707f5168f5888b2446a4518426bb04
Upstream bug: https://unicode-org.atlassian.net/browse/ICU-21875

Bug: 194885609
Test: atest CtsIcu4cTestCases
Change-Id: I69425d2cae2e9c7006a0261dc991d8d7b07e5cef
(cherry picked from commit 93d9317dd472368835a7e5f457cc7a69bc2e4437)
Merged-In: I69425d2cae2e9c7006a0261dc991d8d7b07e5cef
4 files changed